1. Field of the Invention
The present invention relates to a method of molding a golf ball, and more particularly, it is concerned with a method of molding a synthetic resin cover enclosing a core of a golf ball, or an upper or intermediate synthetic resin layer of a multiple-piece solid golf ball. The present invention also relates to a golf ball molding die.
2. Description of the Prior Art
Solid golf balls such as two-piece golf balls are usually constructed of a spherical core which comprises polybutadiene rubber as a main component and a cover enclosing the core which comprises a resin such as an ionomer resin as a main component.
The conventional method of molding such a golf ball comprises the steps of standing three or more support pins in the cavity of the mold, placing a core thereon such that it is positioned at the center of the cavity, filling a cover-forming material into the cavity, i.e., between the core and the inner surface of the mold, and curing the cover-forming material.
At the time of molding a golf ball according to the above conventional method, if air is sealed in the cavity of the mold upon filling a resin (cover-forming material), the resin filled lacks continuity, and this causes such defects as scorching, air mark, weld, and the like.
Therefore, it is necessary to evacuate from the cavity, air and gas which is generated from the filled synthetic resin. To this end, the conventional molding is carried out by providing the mold with a vent hole and evacuating air and the gas by natural ventilation through the vent hole from the cavity.
FIG. 1 illustrates a lower die A of a conventional mold for golf ball molding, which has an air vent pin 1 inserted in a vent pin hole 3 and a support pin 2 inserted in a support pin hole 5. A core 10 of a golf ball is placed on the support pins 2, and then an upper die B (the same construction as in the lower die A, although not shown) is closed. Thereafter a synthetic resin for forming a cover is introduced into the cavity (between the inner surface of the mold and the core 10) to injection mold the cover. In this case, the internal air and the gas emanating from the synthetic resin are discharged from the cavity by natural venting through the clearances between the air vent pin 1 and the wall of the vent pin hole 3 as well as the support pin 2 and the wall of the support pin hole.
In the natural venting method by vent holes provided for the mold, when the plasticized synthetic resin enters into the cavity, the air in the cavity and the gas emanating from the synthetic resin are pushed out and discharged through the vent holes from the cavity. However, if the vent holes provided for the mold are too small, poor venting results, causing such defects as scorching, air mark, and weld. On the other hand, if the vent hole is too large, the resin flows thereinto and is cured as such to form a flash, and substantial labor is consumed for finishing to remove the flash.
It is a usual practice for filling the synthetic resin into the cavity to employ the injection molding method. However, if the injection speed of the synthetic resin is too fast, the speed of evacuating air and the gas from the cavity by natural venting does not catch up with the injection speed, resulting in the remain of air and the gas in the synthetic resin, and this also causes such defects as scorching, air mark, and weld. Therefore, it is difficult to speed up the step of injection molding so fast in the conventional method of molding a golf ball.